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Designer Update to the Carbon Rig for 29er

Update on Carbon Rig for 29er

Std rig and the Mk7 rig in Austria May 2017.

Wednesday, 11 July 2018 – Sydney

Preamble:

November 2017, after spending a considerable amount of time in Asia and Europe looking at the existing rig, I moved several spec changes to resolve “cannoning issues” (topmast moving into the mid-mast, and Mid-mast into the lower mast) in the Alloy mast and these were reviewed by World Sailing and the Class and I believe they are now approved.

First few months of 2018, given the damage to upwards of 52 near new jibs in one day, at the HK Worlds, a new reinforcing design, very similar to what worked so effectively on the 49er, was proposed and I had 2 of these jibs made and they are now in Europe.  We titled them “training jibs” based on the NZ/Aust usage.

April 2018, so they could be discussed during the builders meeting in London May 2018, I proposed several other changes to the Alloy mast again to ensure that with the impending Chinese order and the level of use these boats would get, which is likely to be double or triple anything that anyone has ever subjected a 29er to, they would stand up.  These are all fitting substitution changes, so like for like, just a different manufacturer/source.

May 11th in the WS offices we had our builders meeting and as is customary, towards the end we were joined by the exec of both the I29erCa and I49erCA.     Joan, Barry, Marcus, and David all joined us.

Right at the end of that meeting, questions where asked about the “training jibs” and about the Carbon Mast.

Until this point, from my point of view, carbon masts were off the agenda.

To cut a long story short, I was urged to request a spec change, which I did sitting alongside the President and Exec Sec a few days later at the ensuing World Sailing conference.   Others were going to contribute, but to date, none have.

18th May I was in HK, the topic of the builders meeting came up, the possible position of a new mast and new sails, was brought to light, this was passed onto the commercial partner in the Chinese program and they have enthusiastically endorsed and adopted both the “training jibs” and the new Carbon mast.

20th May, the tech officer of the I29erCA started the “training jib” spec change process, 21st May WS responded.    I don’t know where this is at.

I have painted a “grim” picture of the likelihood of the Carbon Rig’s acceptance by the I29erCA to the Chinese purchasers.  I have been quite explicit on 4 occasions, and 4 times they have come back and confirmed their wish to proceed with their commitment to the Carbon mast.  The last occasion was Tuesday July 10th.   This has now been confirmed in an email.

The way it presently stands, we will be supplying the impending initial Chinese order with upwards of 20 Carbon rigs and 40 “training jibs” to Shenzhen in September 2018.

Because of the Chinese commitment, we presently have orders for another 5 29erCRs outside of China.

Where we are at

Re the Mk7 rig, featured above, is in Arco, Lake Garda in Italy. I took the time to go and have a very good/hard look at this rig on June 30th, several weeks ago, and it’s in remarkably good shape for a rig that has seen 4 years of use across 6-7 countries on 2 continents.    It was not on a boat, but I see no reason why it could not be used at very short notice.

The Mk8 rig is in my front yard in Sydney, it was stepped in a boat a few weeks ago, measured, and it will have sails in under a week which will be tested before going to China as templates for the Chinese order.

Re Helsinki, we have run out of time and given the present climate, neither I nor either rig is likely to make either meeting of the WC or Exc at the Europeans.

The differences between the Mk7 and Mk8 rigs are very minor (see the back page).  The Mk7 rig is approx. 140mm taller than a std rig and has a semi squarehead/pin head mainsail profile.    The Mk8 rig is only 75mm taller than the std rig and has a full squarehead mainsail profile approx. 750mm in width which is very similar to a 49er in luff-length to head length ratio.    Based on everything Ian Macdiarmid (the sailmaker) and I know, the 29erCr will behave like a 49er rig, less like an 18teen/FX rig.

As for the rest of the measurement WRT the Mk8 rig, Goosenecks [GN] are the same position on all the rigs, the rest, in most cases 100mm higher than the std rig, 20-30mm lower than the Mk7.

Standard jib sits on the MK8 mast, the clew rises 2-3mm. The standard spin also flies off all the Mk8 Mast, you just want to tie a knot in the halyard 100-120mm down to get the correct flying shape.

The reason the forestay is higher on the Mk8 rig, along with the shrouds, is it’s the only way to get the mast to behave correctly.   That is also the reason for the introduction of the D1’s which go through the vang GN, (photo front/back page) no extra holes and the D1 is made of rope/spectra/dyneema.   The reason for that is that square heads need greater control over the lower mast and rope D1 is a very effective and inexpensive way to do it.  The 49er experience is you almost never move the D1’s, they are very much set and forget, so on the 29er they are simply anchored via a sliding splice to the existing chainplate adjuster.

Rope is also far gentler on the body.

With the rig, I have taken a comprehensive approach, so I have looked at everything above the gunwale.   Hence spectra D1’s etc.  We became aware if we re-model the boom section, using slightly increased wall thickness, ensuring continuous curvature would lead to a reduction of the price to 1/3 of the existing section, also losing 20% of the weight and almost no strength.    We have “borrowed” this technology from other projects like the c5 Laser rig.  (it is a c5/c8 Laser boom).  Other similarly borrowed technology includes a vastly simplified ram vang system.   One of these changes is that just about no one adjusts the outhaul, so we will couple that to the vang, pull the vang on, outhaul also comes on, let it (the vang) go, outhaul eases.

But, given shortness of time, we are cutting up perfectly good 49er spreaders to make 29erCR spreaders, very expensive way to do business.   We obviously expect given the fullness of time, the cost of these will drop significantly.

And we intend to borrow from the Laser class (similarly the 49er class is likely to adopt) a “compliance model”, which means we set a standard of compliance, very tight and anyone who can prove they can make a component to that standard is given a license to produce.

I will touch more on this later re costing.

Weight of the standard rig is 10.4kgs, Mk7 rig is 7.8kgs, Mk8 rig is expected to be about 7.2kgs.

Re reports and data, there are about 400 pages of written reports on the rig going back 8-10 years.   Then there is a plethora of data records.

Possibly the best compiled document is the thesis by Gottfried Gerhard Klampher, from the Uni of Vienna, Austria, which is in the public domain, completed earlier this year.  On the following pages I have referenced the key graphs, but the thesis is worth the read regardless.   It’s about 80 pages.

Above is the boat going to windward, the top graph is the unfiltered data, the lower graph is the same data but with significant dampening so as to generate a trend.

It’s very early days, and the new rig is not that well known, but the overriding thing which shows through is that the new rig is not so much faster but it’s a lot smoother, it’s easier to sail and the boat doesn’t slow down anywhere near as much.

If you look at the top graphs, time and time again both boats drop in speed, but the carbon rig boat drops less and recovers sooner and more than the current standard rig.

The wind in both these set of graphs is approx. 10-12 kts and the more consistent speed is common   across most wind strengths.

The 2 boats were within 10-20m of each other when this data was collected.

Below the upper graph is going to windward, the bottom graph is coming downwind.

Same wind as previous graphs.  Boats again were within 10-20m of each other (except the tack).

These are TWA’s (True Wind Angles)

Upwind, in the steadier starboard tack, both at the beginning and at the end of the graph, the Carbon rig holds a far steadier and higher AWA than the standard.

Downwind is more telling, the Carbon rig’s VMG is markedly better, both gybes.

 

The following is an attempt to pre-empt questions.

Why extra length of the mast and extra area?

Because if we do nothing, just switch the mast, we know the crew weight will drop approx. double/triple the reduction in rig weight.    This is true regardless of whether it’s an I14, 5o5, FD, 49er, Moth, B14, Cherub or a 29er.    It’s a very simple sum to increase the area and the “arm” (length of the mast) to restore the weight.   See the email towards the end of this document.

Why a square head?

If we had 1 million years to evolve the rig, then we would closely approximate those that have been at it for 1 million years, the birds and fish.     But we are mere mortals and we are not that good, so we try to approximate an ellipse (Spitfire wing tip or the wing tip of a 787 or A350).   Our material science is still primitive, and people bounce mast heads on the ground, so the top of the mast is bigger than it needs to be, it is simply not flexible enough to do a really good job, plus it’s heavy.  So, we start trimming the mast height back, we “truncate” the rig, we end up with a square head, and if it’s done well, we can achieve something special. A very elegant solution especially for all sailors.    For those just coming to grips with the 29er, it’s easier and it also allows those with experience to push the rig further into places they would not normally go and have fun safely.

Why Carbon?

Materials have changed, carbon is getting increasingly cost effective, particularly with respect to longevity.   The biggest advantage is environmental and cost effectiveness with time.    When you buy a 2nd hand boat, with a carbon rig, it’s almost impossible to “buy a lemon”.

Alloy yields every time you bend it, does not matter which alloy or what industry, which is why most aircraft must be retired after X number of cycles.    Well-designed carbon structures do not.

Carbon is smaller and lighter and the rig is ready.

Need to touch on inertia, it’s possibly the seminal point.   Sure, the rig is 3-4 kgs lighter, and in itself, that weight difference is important and real, but once you turn that into inertia, it becomes significant.

When you apply the inertia rule to all the other carbon rigs out there, it explains just about everything we empirically observe. That plus the air-dam factor, it all starts to make sense.

So what’s inertia?  You’re driving down the road, a cat runs across, you slam on the brakes, and you lurch forward into the seat belts, that movement forward is inertia.

Inertia is a X² law.

I know that the 3 Carbon sections of the Mk8 mast weigh 4.8kgs.

Therefore the “bits” – wires, spreaders, ropes fittings – weigh 2.2 to 2.4 kgs.

So the alloy/FRP section of the alloy mast weighs 7.8kgs, approx.

Reason for the maths is there is a simple way to do this sum and a complex, I like it simple.

The bits are constant, the height of the bits, the sail, so if we just look at the X² of the sections then we have 8² = 64 and we have 5² = 25 (I’m not good at SI units but I’m guessing this is Newtons).

Doing it the more complex way, include the whole mast, wire, ropes and bits, so the whole Mk8 mast weighs 7.2² = 51.8 & std mast weighs 10.4² = 108.16, we can add the sail, but it’s still <½ the inertia.

Call it Newton’s, whatever you like, the carbon rig has ½ the inertia of the alloy rig.

And yes, all sorts of exceptions and rules are being broken, the hull weight is in there, and the mass of the crew etc, but comparing apples with apples, it’s ½.

What does that mean?  When you go through a gust-lull sequence, and the rig starts heeling and then coming back upright, the amount of energy to stop the rig’s inertia is significantly less with the carbon mast than it is with the alloy mast.   This is sometimes referred to as “radius of gyration”.

Put an 8kg lump of lead on the end of a 3m pole and hold it with one hand, upright and walk about. Now the same pole but with 5 kgs of lead, walk about.   This is exactly what we are talking about.

The 2nd thing is air-dam, or it’s occasionally called a flipper-head.

Go get the bit of cardboard off the back of an A4 pad, curve it a bit and drive down the road at 35kph (7knts BS + 12knts WS = about 17knts AWS.  1knt = .55m/s = 2kph, so 17knts = approx. 35kph) and stick the bit of cardboard out the window and fly it.   Now rip ½ the top corner off approx. 45° and do it again. It becomes very obvious that the square head bit of cardboard generates more resistance.

Go from cardboard to Mylar, get particular about the “trigger” point of the #1 batten (known as Euler crippling (or buckling) load [ECL]) and what happens is that the whole inertia thing (due to the reduction in weight) is enhanced quite dramatically by the air-dam of the squarehead.

The net effect is you’re a young gun, silver fleet, out at the top of your range and you get hit by a gust, even before you ease the sheet or luff, the load in the leach goes up exponentially (it’s also an X² law) and the compression in that top batten goes up also as a factor probably in excess of X².

First thing that happens is the mainsail flattens off, right at the head where the most amount of righting moment (heeling) happens.    And normally that is enough, but if it’s a big gust, then as the load continues to increase, almost regardless of mainsheet tension it will continue to de-power and may even “trip” to leeward (if you exceed ECL).  If you’re skilled on the mainsheet this whole process is enhanced, and the trigger point can be set via vang and/or downhaul tension.     If you’re in the upper level of the weight range you keep the mainsheet on longer, then start using the vang, delay downhaul.  And if you’re light, you come down harder on the downhaul earlier, start easing sheet while drumming on the vang.

Then as the gust goes away, the reverse happens, if it has “tripped” (1st batten) it pops back, and powers up, faster than you can squeeze the mainsheet on.

The net effect is the boat becomes far easier to sail, with a wider weight range and it simply does not slow down nearly as much as the pin-head rig which the boat presently has.

So yes, simply pulling 3-4 kgs out of the system lightens the boat, there is less drag, but that’s really only a 1 – 1.5% impact on the overall weight of the boat, and that = faster and/or higher, but the big difference is the boat is far more easily driven, so it just does not slow down as much and it’s that much more fun and that much easier to sail!

Supply of carbon fibre (i.e. shortages).

Fourteen 787 aircraft are made a month, the whole plane weighs 120 tonnes (empty) and approx. a quarter of that is Carbon.

So that’s a little over 4,000 tonnes of carbon a month and we have not even started with A380’s, A350’s, military, medical, automotive and even the humble phone cases.

We are talking about using maybe a 1-2 tonnes of carbon a year with the 29erCR and the likelihood of there being a shortage of supply that will impact the sailing world is miniscule.

Booms

Both boom and vang systems can be used with either rig, you just have to switch out what we call the knuckle, and it can be switched back later.   We will make a “special” knuckle so existing booms/vangs can be used with the Carbon mast.   We can supply it with the rig at no extra cost.

The knuckle used on the 29erCR is the same one used on the existing 49er rig.

Other Developments

Some of you will have heard about the c5 Rig on the Laser, there is also a c6 and c8 rig.    Prof Tracy Usher, the Pres of the ILCA has been recently quoted as saying “we don’t see white sails and alloy masts in our future”.

The c5 Rig borrows most of its technology from other developments, across a range of classes, this is ongoing evolution.  All that being said, the Mk7 rig is still relevant, 4 years on.    The Mk8 rig will be a refinement of the Mk7 and it will be equally relevant for the foreseeable future.

The Mk 8 rig borrows technology from a wide range of sources, some unexpected and some more logical.  It cuts both ways.   The 49er class is presently undergoing a rig refinement process, including the “compliance model”.  I am working with Southern Spars initially, a lot of the development work that has been trialled for 4 years on the Mk7 will find its way back onto the 49er in the next iteration.  And that in turn will refine and improve the Mk8 rig, the c5, 6 & 8rigs and so on and so on.

The jib and the spinnaker need not change.   There is almost no need to change the jib beyond the ongoing spec change, the “training jib”, to include the zipper and extra reinforcing.   That is going to happen anyway and it may well be cheaper (zippers are cheaper than hanks).

There is an argument to change the spinnaker, it’s an 18 year old design, and if the spec change is unsuccessful, that may well happen quite quickly.

Logistics

The existing 29er mast in NZ is the most cost effective because it does not have to be transported around the world.  All the raw components of the mast come from NZ.  The most expensive place is the USA, because the components have travelled 3/4’s of the globe just getting there (and NZ have the most expensive complete boats because the hulls have to be imported from the UK, as a result, they are about to start building in NZ again so this will change, it’s just a question of logistics).

The Laser based compliance model which is already in place with the new Laser carbon topmast, we believe will result in Ovington sourcing more 29er parts in Europe, Zou Marine producing parts in Northern China all compliant, etc, all within a very tight band of tolerance and all cost effective.

It will also allow manufacturers to “pick and choose” where they purchase parts from, so shortages will be a thing of the past and this process will also transparently drive costs down.

But there is no way around the fact that to produce 3 carbon tubes is more expensive than extruding 2 bits of alloy with multiple sleeves, (& a FRP Tip) but by designing everything in, so there are no extra bits to be added on, we have cut the rigging time by more than ½ and we have increased reliability and repeatability dramatically.

This could be called the Ikea model, that being, because there are no sleeves, the 3 sections are tracked and fully machined, they are 100% complete, to the same spec pattern, it can be assembled with an Allen key in about 3 hrs by anyone, coaches, sailors or parents, so it’s bolt together, much like Ikea furniture.    It also means that we can supply every bit in its simplest and therefore at the least cost to the end user.   Think spares!  We can also adopt an Amazon supply model, so if for whatever reason a part can’t be obtained in San Francisco, it could be FedEx-ed over night from HK (or UK or Qingdao) so you can go sailing on the weekend.

Re introduction

Firstly, it simply can’t happen before September 2019.    The planned (and they are very good at it) ramp up of Chinese demand would suggest we will be “many” 29erCRs in China by then, and for me to manage that and worldwide demand is just not going to happen.    The up-side is we will have a near perfect supply system in place, initially out of HK/Shenzhen and operating in a “closed’ market like China, all the bugs will get ironed out before the rig goes world-wide.

The experience of the 49er class with a far more expensive “switch cost” was that over 450 complete rigs were ordered within the first 9 months and that was over 10 years ago.    It sent Southern Spars into a tail spin that we are only now sorting out properly.  The bugs had to be fixed on a global scale.

Those people buying a new boat in Europe, it will be a few % more expensive (the rig is about 1/3 of the cost).

Those in NZ will hurt the most, about 5% more (until they start building again).

Those in USA will be marginally better off, those in the UK, a few % better off.  AUS, no change.

In the event we can plan, and consolidate orders, prior to acceptance, then there is every likelihood that those bonafide sailors with existing rigs could get a 10% bulk order discount for 5 or more rigs.

The difference between what is being proposed here is what was stated above, there is likely to be quite a lot of 29erCR rigs in China by the time we adopt this, so the ramp up can be far more efficient!

At the end of the day

The really big winner in all of this is the boy or girl who buys a 2-3 year-old boat.   Other than a bit of TLC, some spit and polish to make it shine, they can go and play hard knowing that the mid-mast has not gone soft, that the top-mast has not “got tired” and the lower mast is not “kinked”.    As I said before, near impossible to buy a lemon with a carbon rig.

Mum and Dad will also be the big winners, no more coaches telling them they need a new mast, the mainsails won’t be stretched from pillar to post, they will last longer also.

It’s a simple empirical fact, we are selling a lot more 49ers these days, and the number of topmasts being sold is a shadow on its former volume, post the carbon rig.   That’s a simple fact and easily checked.

And the rock-star will have a rig that will set him/her up for his/her progression to the FX or the 49er or anyone of the other hi-end boats, even yachts, and he/she will have a ball doing it.

Have a great meeting.

Julian Bethwaite

~~~~~~~~~~~~~~~~~~~~

The following is an email that explains the workings on the next page, a few have asked how did I get there.   It’s very simplistic, but its backed by more complex calculations.   Maka = Ian MacDiarmid

From: Julian Bethwaite [mailto:julian.bethwaite@upmarine.com]
Sent: Wednesday, May 30, 2018 3:57 PM
To: Ian Macdiarmid ; Joan Mollerus ; JOHNSON Barry ; Chris Turner ; Carlos Debeltran ; John Clinton ; Mark Paul
Subject: 29erCR mainsail

Hi all,

Just had a phone call with Maka, we are very short on time WRT getting a main done in time for Helsinki, so I have just spent a few hours doing some maths and working this all out.

Barry, you will need this for the Spec-change.

Just keeping it as simple as possible.

The new CRig will be about 3 – 3.5kgs lighter.

History tells us, that if you do that, you lose about double that in crew weight.

So if we do nothing, crew weight will go from (and here you have to pick a number) 130kgs to 123kgs, or 5.4%.

If you take the existing UW sail area, (12.41m²) and factor that up by 5.4% you end up at 13.116m².

Take the jib away, because that’s not changing, you end up at 9.35m².    And then factor that back by the increase in arm of the mainsail, from 3.35m to 3.5m or 95% and you end up with a target mainsail area of 8.9m².

That’s the simple maths, I actually put this into a far more elaborate formula that my father and I have used for years, using radians, and lbs/ft, etc, and the sum is almost the same.   So I am moderately confident.

We can’t get there without increasing the mast height 50mm, and even still the headboard length is becoming quite long, up around 38% and I don’t want it any longer (FX is 42%, 49er is 28%).

We may use an end-plate on the mainsail to extend the weight range further up, without hurting the lower range, but that will be a suck it and see exercise.

Maka, if you want a more detailed DWG with lots and lots of measurements, I can do that.     Also, I have no doubt that other programs will measure things differently but I am measuring like for like, so it’s all relative.

JB

Red = existing standard rig, yellow = Mk7, blue = Mk8

The cuff at the bottom will be enlarged based on the experience of our testing and the AC and A-Class cats development.    The rig will very likely have winglets also, again from our testing.

Boom Gooseneck with vang sheave incorporated, similar to 49er system

Masthead fitting with GoPro mounts front and back, bigger sheave, M6 axle, and track capture

Mast gooseneck, bolt on with Allen key, radius slot at top to accept rope D1, 2 holes at bottom for exit of halyard, again radiused so as to act as low friction ring.  Grooves in base increase glueing surface area.

Square head vs pin head rigs

Square heads have been around for thousands of years, Vikings and the sails they had on their long boats, and I’m sure the Polynesians and their Proa’s preceded that also.

The Dhow Rigs are equally as old, “leg of Mutton Rigs”, formed into the original “Bermuda Rigs” in the 17th and 18th centuries.    Then came “Gaff Rigs”.

What I refer to as a Pin Head rig is really a Marconi Rig, developed mostly in Germany at the beginning of the 20th century.  Most notably “triangular sails”.  Manfred Curry in his 1946 book shows lots of photos dating back to 1935 of his father’s boats, and those boats had developed significant “roach” (curvature in the leach of the sail supported by the battens) and a level of mast bend.

I will now skip 50 years of development and I acknowledge that this is a great dis-service to many developers including my father.

In 1981, I tried and sailed a 2-handed 18 foot skiff (Prime).  Over the next 3 years that developed and what became apparent was with only 2 people, you simply did not have enough hands to do everything, so we needed to make the rigs automatic.


2-handed Prime 18ft skiff

The development happened at an extraordinary rate, 10 years later a GRP 18teen with a few carbon straps (to hold the mast), went around the std NE course in Sydney Harbour in under 50mins.   The “straight line” distance is 15.5nm, it was a heat of the World Championship, 3 windward legs, 2 downwind legs around the island, 1 straight to the bottom, not too many gybes, but plenty of tacks.

Sure, it was a highly refined boat, many aspects of it were honed but the biggest contributing factor was a highly developed “pin head” rig!    That record time still stands today and not even foiling Moths or MC32s can come close to it.

I doubt a square headed boat will ever be able to achieve that sort of time for a few years to come.

So, the very refined “pin head” rig was a bit of mathematical poetry.

First issue was the way the mast bent, biggest contributing factor was the height of the hounds, and altering this 20-40mm (in a 10-11m mast) made considerable difference to the point where there were 2-3 keyways (attachment points) for the forestay that could be selected depending on conditions.    We always tried to get an “exponential” bend, so the lower sections (alloy tube) bend far less than the upper mast (GRP wound tube).   We developed a whole system of % and depth to define this bend, and we would alter it by 0.5% occasionally.

Once we knew the luff curve of the mainsail, and the rate at which it would bend under different loads we then designed the roach of the sail.      They had to match, and there was again a very definite multiple, so if say there was 222mm of luff curve, we would have 222 x (say) 3 = 666mm of roach at that height in the sail.

 

© Sport the library/Jeff Crow
Sailing-18ft, Hayman Island 1993
AAMI/Mast Mount
1993-0010-8621-157

So why am I going into such detail?

Because of the analogy of a gust, and what do we want to happen in that gust.

Your standard gust lasts 9-12 seconds, it increases the wind speed on average by 25-30%.   So, if the mean wind is 10kts, then the gust is likely to be 13kts, and in 99.99% of cases, it will be skewed 3-5° off the mean wind direction.   The reason for that is it comes down from the layer or 2-3 layers above, and almost by definition those upper layers are screwed by Coriolis, so they are at different angles to the lower layer of wind.

But the most import thing about a gust is 80-85% of the energy is in the first 0.5-1sec.

You’re sailing in 10 kts, fully powered up, gust hits at 13 kts. Force goes up by X² so it goes from a nominal level of 100 to something approaching 169, and it happens in under 1 sec.    Do nothing you capsize, simple.    If you’re good and you can see it, you luff a little, and your sheet hand prepares to ease the sheet.   Get it wrong, you capsize.

With an automatic pin head rig, because the load increases, the mast bends more, and it bends more at the top than at the bottom.  If you have the roach right, then it progressively flattens at the head more than it does at the foot, so the CoE automatically drops, increasing your Righting Moment, and that in turn helps to “resist” the increase in force and again this all happens in under 1 sec.

The other side of the gust, the automatic rig also powers straight back up, long before even the fastest human being can tension the mainsheet.

By the time we got to 1993 and the AAMI 18teen foot skiffs, we had it, so you were actually pulling the mainsheet on in the gust, which meant the rig automatically flattened even more in the gust, which led to much higher pointing angles, and acceleration.

The “pin head” rig theoretically closely approximates an ellipse, therefore as you move towards the tip, the span-wise “pressure” loading drops and you minimise tip losses, vortices and the like.   If we were as good as the birds, we could probably effectively end plate with all the aspect ratio benefits that brings.

But we are nowhere and will never be as good as nature and the birds!

The first time I saw a square head rig was in the late 80’s.   Chris Cairns’ loft was upstairs from our factory and he was using the square head to try and emulate what we had with the pin head rig but on a Tornado which at the time had a tree trunk of an alloy rotating section mast.

It would not bend, so he used the bias of the sail cloth and the square head to emulate the head de-powering benefits of the pin head.  It was very clever, and it required some quite extraordinary detail in rocking the head panels to get the desired result.   We still do this today in the 49er mainsail.

With the advent of carbon masts, the ground rules changed.   The UTS (Ultimate Tensile Strength) of carbon and glass are in fact quite similar.  What is different is elongation to break.    Glass, if laminated, with epoxy or vinyl-ester is 5-7%, good Carbon is 1%.    It’s just a whole lot stiffer.   If you are looking for a mast to bend consistently at 4-5% and you’re using carbon as your base material, you either need to thin down the wall thickness or reduce the diameter.    But the overwhelming reason for using carbon is weight.   The base tube weight is approximately ½ that of its alloy counterpart and ¾ of the weight of the GRP topmasts.   And now, with advances in building techniques the cost is coming right down.  In 5 years’ time, any relevant class will have a carbon mast.

Thin wall tubes are fragile, so in 90% of the cases in the marine mast business diameter has dropped 15-30%, wall thickness has gone up from around 1.7mm to 2.2-2.5mm and this new breed of carbon mast is now extraordinarily tough and light with huge longevity.

But, the topmast simply does not like to bend anything like the old GRP topmast.

At the same time material science has evolved so that the Mylars used in sails have similarly advanced, and the extent to which you can dial in bias, warp and weft is simple and common place, especially if you are buying 1000’s of meters for classes like the 49er.

What we now do is design the bias stretch, we rock the head panels so we get the warp/weft aligned exactly and then complement that with the bend of the carbon mast to achieve something approximating the sort of automatic gust response of the pin head rig.

There is a lot of science to this.   The biggest contributing factor is the length of the square head.   Most sailmakers like excessive squarehead length.   Our experience of the 49er and FX sail plans, is that if you go too big, you lose “range” and the ability to alter the shape beyond a rudimentary level.    In the 18teens which are even more extreme than the FX, this has become very niche, they are fast in one setting and they sail the boats, so they are in that setting as often as possible.

This is not necessarily a bad thing, it’s evolution, and that process has many years to run.

If you get it right, then you may also endplate the top of the sail effectively, and that leads to Aspect Ratio benefits and considerable changes to CoD and CoE considerations.

Going back to the 18teens, they are pursuing this now extensively with mast head battens that are not too dissimilar to a 787-wing tip which when all is said and done, are copies of birds, think cranes at altitude in gliding flight.

We still have a long way to go, it will get refined further over the next 5-10 years.

It’s been 25 years since we put a cuff on the bottom of a 49er main, that is still surprising us as to its effects, square-heads will be a longer road yet again.

Julian Bethwaite
November 2017

Forthcoming changes to the 29er

Being immersed in 29ers via Asia and southern central Europe and forecasting the boat’s use in 3, 4 and 5 years down the track, I would like to propose the following changes.

Three issues are affecting the long-term use of the 29er, and those are:

#1 – the cannoning of the mast sections into each other, under ever increasing rig tensions

#2 – switching to a new 49er style gooseneck should be a foregone conclusion and is just housekeeping, we should have done this years ago, but put it off so it was done at the same time as the carbon mast which obviously isn’t going to happen anytime soon

#3 – the deterioration of the watertight seal of the scuppers particularly in the Asian environment but is also now starting to show itself in southern USA & northern Australia

In detail.

#1 Cannoning of the mast joints.   This is the movement of the top-mast downwards into the mid-mast and the mid-mast into the lower mast, under increasing rig tension loads, in part because the boat is being pushed harder by the latest generation of sailors and in part because of the introduction of the turnbuckles, again because the boat is now being sailed by a more determined group.

Simply, the existing array of bolts and “spreader bars” are not sufficient.

Mid-mast into lower-mast is by far the simplest, there is already a sleeve there to anchor the spreader, we just need to increase the number of M6 MT (metal-thread) bolts by 50%.   Better still if we use CSK (countersunk) heads on the additional bolts as these will spread the load onto the 1.71mm wall of the lower-mast more effectively.

In detail, the internal sleeve that is used to anchor the spreader and secure the mid-mast and lower-mast together would be lifted 20 mm, and secured as it is presently.   The spreader would still be attached in exactly the same way and in addition to that in-line with the bolts attaching the spreader, approx. 20mm above the spreader we would add 2 x M6 MT CSK bolts going from the lower-mast, through the mid-mast and into the sleeve.   They would be approx. 10mm in length.

The top-mast into the mid-mast on closer examination is a little more complex.   There are 2 movements.    1st is the securing of the existing sleeve into the FRP top-mast.  Because it flexes, the existing sleeve moves inside the FRP laminate, there is nothing holding it (the sleeve) hard against the inside wall of the FRP, hence my comments above about going to a t-ball for the trapeze wires.

I have considered approximately 6 different options to secure the sleeve, and in terms of retro fitting and in terms of going forward, switching to the use of a t-ball and key plate I believe is the best solution.

By switching to a key-plate anchor, you have 4 x M5 rivets holding the alloy sleeve hard against the FRP tube.    We know that 4 x M5 rivets is enough to withstand about 4 tonnes which is more than you can ever subject a 29er to. Retro fitting, the ID of a Keyplate is 8-10 mm, the hole is 8-10mm, it is accessible from the joint, it can be done easily.   Even just adding 4 x M5 rivets approximating the position of a key plate above and below the existing spreader bar would dramatically alter the structural integrity of the sleeve/FRP joint.

T-balls are well known, simple, cheap, there could be even a negative (as in cheaper) cost consequence of the change.

Once you secure the sleeve into the FRP, then adding 2 x M6 MT CSK bolt, in nearly exactly the same way as I am suggesting we do at the Mid-mast/Lower-mast interface should take the structural integrity of the joint above the critical level and arrest the movement.

#2 Adoption of a 49er style gooseneck.    The kids are driving the boats harder, there are tell-tale signs of stress at the front of the boom. And the biggest bug-bear of the vang shoe falling off, especially in older boats, simply goes away.    6mm pin, it’s simply “fit for purpose”!


Proposed 29er gooseneck


Current 49er boom gooseneck, proposed for 29er boom

I would also seek to use grommets for the mainsheet blocks as people are moving to lash on blocks and the grommets are far more structurally sound.    They are already used on the Tasar boom which uses the 29er section and it has stopped their boom breakage problems.


Proposed 29er boom grommet

Sourcing parts direct from source will also be refined.    The alloy for instance could be milled at source in NZ, reducing weight, length, so enhancing logistics, and dramatically enhancing replacement options and the one-design nature of the boat.       We have already done this as a test with the 49er boom, reduced rigging time by 75% with the obvious reductions in costs.

Finally, it will be my intention to use the appropriate “fastenings” where needed.   If we go for T-Ball/KeyPlate trapeze then it is appropriate to use rivets.    In a lot of other places, it is appropriate to use MT’s.     This has to do with access (or rather lack of access) to riveters in many parts of the world.

#3 Scuppers.    Recently we replaced the post moulding screw on foot-rails with moulded in foot-rails.   The rationale was simple, that the screw on foot-rail was the source of many leaks, they were a source of on-going maintenance and a major cost to install and to warranty.

The resulting moulded in foot-rails do exactly the same job, but simply do it so much better.

Until early this year, we believed we had overcome all the major issues surrounding the scuppers, the switch to MMA adhesive, new mouldings, etc, gave us great hope.

No question they are better, but they are still not perfect.

In humid tropical climates, we are still getting rot quite quickly and even in LA, a 3 year old boat required complete replacement of the scuppers.

Therefore, I intend to replace the scuppers with a trench.

The similarities with the foot-rails are near identical, rather than post fitting, it’s moulded in, and the financial benefits (savings) are far greater with the trench than the post-fitted footrails.

It will do exactly the same thing.   And by my calculations at near exactly the same rate.

In detail, directly under the top rudder gudgeon, we would mould a trench from the top of the transom bulkhead, down to the top of the cockpit floor.  It would be approximately 60mm wide at the cockpit floor (+/-30 mm per side), growing to approximately 70-75mm wide under the top gudgeon plate (draw angle).    Basically, where the World Sailing hull number plaque is presently placed.     There would be suitable radiusing of the corners, etc.  We would also “let in” the new alloy top rudder gudgeon (see below) so the depth of the rudder stock does not alter.

We would replace the 2mm thick SS top gudgeon plate with 6mm Alloy plate and secure it with 2 x M8 MT CSK bolts each side (this is exactly the same sort of plate that we use on the SKUD).


Proposed trench at stern, looking aft


Proposed trench at stern, looking forward

There would be no changes to the angle of the rudder, the rudder stock or the placement of the drain bung, as the bottom of this trench is about 50mm above the transom flange.

The result will be no rot to speak off, no leaks, nothing to work itself loose.

Longer term, considerable cost savings, as there is no 2nd fitting, there are no 2nd mouldings.    The only fitting change is you screw down an alloy plate rather than a stainless plate.

These changes will be open for discussion at the LA World Championships 2017.

Julian Bethwaite
10 June 2017

Jib Sheeting Angle

Julian Bethwaite – Saturday, 7 January 2017

(Click on diagrams to enlarge)

Jib Sheeting

Just before Christmas, I spent some time in Mumbai India, coaching 9ers.

Last time I was in Mumbai was 3 years ago, and the place has improved dramatically, there is a very positive energy in the air, and I was only accosted by a beggar once in 5 days.  Quite extraordinary!

Lots of questions, feel, balance, sheeting angles, what the wires do.   Due to the Nationals being scheduled in Chennai for the 29ers, we had 8 49ers and a few FXs in Mumbai, so it ended up being very 49er centric.   The sailors were from Chennai, Bhopal and Mumbai, mostly, some Navy and Army node sailors also.

The English did leave India with English as the binding language, but it’s not the mother tongue. There are 2000 different languages/dialects across India, and that makes some of the answers more interesting in that you must get the idea across to a body of people in a manner they understand in my limited Australian.

On the first day, we laid a boat on its side and started to explain what each control did and the importance of batten tensions, but a question that came back time and time again was jib-sheeting angle.

A 49er/FX is a lot more complicated than a 29er in that you are allowed an adjustable (not while racing) jib tack length.   The 29er is a lot simpler, in that it must be shackled on in a fixed position.

So to keep this simple, I am going to focus on the 29er, but the 49ers are exactly the same!

A jib is, for all intents and purposes a triangle, and that makes life very easy, in that it’s very easy to find the centre, what we refer to as the CoA (Centre of Area).   You simply bisect say the luff, and you draw a line from the clew to the middle of the luff, do the same thing with the foot, draw a line from the head to the middle of the foot, and where those lines cross is the CoA.

 

This is a 29er jib, done to scale, it is accurate.

The black line shows the edges of the jib, and the cross lines are the battens.

The blue lines are lines drawn from the apex(s) of the triangle of the sail to a point that bisects the opposite side

The green dot just above the bottom batten is the CoA and I have given you measurements so you can actually go and measure this on your 29er jib.

The red dot 91mm above is the Centroid!   I’m cheating in that I am using a 3d program to draw this, so I asked the machine to find the Centroid.  

The difference is because of the roach in the leach, and I use the green position.

 

Now we have the Centre of Area.

That is NOT the CoE (Centre of Effort).    I have just trawled through all my father’s books, Manfred Curry’s “Theory of Wing Section” but the late, great Prof Marchaj probably diagrammatically describes the shift from CoA to CoE the best, so I am poaching 2 of his drawings.

On the right is what my father would have referred to as Piedo Tubes, used heavily in the aircraft industry to sense air pressure, you will still see them today normally toward the front of the Airbus or Boeing, but they are equally useful in measuring the pressure differential across a sail.

This one gets to the guts of it, again courtesy of Prof Marchaj. 

Without getting too involved as to why, if you measured the area under the curves and then found the medium point at which there was equal differential in front as behind, you would find you are somewhere between 30-35% back from the LE (Leading Edge).

When you first tack, let’s say you do a bad tack, the Centre of Effort will be approximately where the Centre of Area is, in the middle of the sail. But as soon as you start to move forward and start getting some meaningful flow across the sail, that CoE sucks forward.    On an old fashion type of sail, a heavy boat, with a big fat knuckle forward, it may suck forward as much as 25% (of the chord) so it will end up 25% back from the Leading Edge.

On a 29er or 49er, which have reasonable size sails and are modern in their design, it finds a happy place about 1/3 back or 33%.

So in the following drawing I have drawn a Cyan line horizontal (because the water is horizontal and it will force the air to “mostly” flow horizontally) that runs through the CoA.

I have then measured the length of that line, divided it by 3, measured back that distance and the Cyan dot is “a close approximation” of the CoE.

So the Red Dot is the Centroid and the Green Dot is the CoA.

The Cyan Dot is the CoE.

If you go get your 29er jib, find a point 60mm above the centreline of your bottom jib batten, measure back 424mm horizontally, you will end up about 25mm (1”) above the batten and that is your CoE.

Extend a line from the clew, thought the CoE, and that should be your “normal” jib sheeting angle.   Draw a line from the clew through the CoA and that should be a “light-air” jib sheeting angle.

For convenience I have extend them forward to the luff!

That is the range of jib sheeting angles that you should be using in 95% of sailing situations.

Why?

The line through the CoE is the easier one to explain!

Notionally ½ the pressure in the jib will be above that line and ½ will be below it, so in the normal gust/lull sequence as increased pressure rolls or passes across the headsail, the load will remain relatively constant, therefore the leach is not going to hang open, the foot is not going to round (fatten) up overly and it should result in maximum acceleration and minimum “stalling”.

Just going one stage further, as that gust-lull rolls across the rig, you are going to ease the mainsheet, and that in turn eases the forestay tension. Therefore you get forestay sag, but at the same time, because your jib has roach, the leach will hang open a little bit more, compensating for the forestay sag.    That hanging open of the leach also increases tension in the jib sheet (as a proportion) along the foot, so it will maintain constant camber over the lower section of the jib (increased load will naturally try and fatten up any sail, stretch, etc).

And all of this happens in about 1/3 of a second, automatically.

It’s the reason we put roach into the jib.

In lighter airs, you don’t want your leach to open up, and because you are seeking power, rather than being fully powered up, an increase in wind speed will allow flow to remain attached around a jib with greater camber, so by sheeting “down the leach” as the gust rolls across the sail, the leach will tighten and the lower part of the sail will fatten up marginally.

So you get more power and provided you don’t ease the mainsheet “overly” (30-40mm is fine) there will be no meaningful sag in the forestay so you can tolerate a tight leach.

Again, because there is roach, the leach will blow open a little, and as the forestay sags a little you will get a deepening of the upper jib, which complements the fattening/deepening in the lower jib and then we can get into all the added benefits that has for the mainsail, and again all this happens in 1/3 of a second automatically.

At the extremes, if you end up in light air and lumpy water, the drag from the lumpy water masks the drag from the overly fat jib, and the extra power may be needed to punch through the slop, so you go even steeper with the jib-sheeting angle.

If it’s blowing “oysters off the rocks” (or “dogs off chains”) then going flatter on the jib sheet angle will allow better control of the lower jib, that you can “drive” off and allow the upper leach to hang more open, allowing de-powering!

But this is less than 5% of the normal sailing situations.

 

In a weeks’ time I will get into Feel and Balance.

There is a lot of the above that is of critical importance to Balance.

Having the boat Balanced or In Balance is possibility the single most important thing you can do.

Unless the boat is in Balance you can’t possibly hope to have any Feel.

That’s actually not true, but your Feel will be masked!

The best way I can think of describing Feel is if a motor car had no feed-back through the steering wheel,  then you can still drive it, but a) you can’t drive it well and b) it’s a lot less fun!

 

Julian

Does JB still go sailing?

The most asked question of last week.

Absolutely, I was on the water on Wednesday and Sunday last week and that’s about normal, plan on sailing tomorrow again, both times on Farr 40s, Wednesday on Exile and Sunday on Estate Master.   Also will be sailing a TP52 on Saturdays when I return from Medemblik (Netherlands).

Over the last 5 years I’ve been sailing multihulls quite a lot, OMR type, 32ft LOA, 27ft Beam, 50ft mast, boat called Trilogy, have had a lot of fun and quite a bit of success in it.

Also some classic boat sailing, 57ft Alden ketch call Wraith of Oden.      Plenty of Laser sailing in the last year, but that’s another story.

And I presently have a 49er on its way to Australia which should be here in September.   Looking fwd to that.   29er wise, last time I sailed one was in Shanghai, last year.

Julian Bethwaite